One popular type of home is what is considered in the construction industry a timber frame home. Timber frame homes are constructed of a plurality of heavy timber frame members and are designed so as to expose the timbers of the frame inside the home.
Traditionally a conventional light frame was built around or between the timbers filled with fiberglass insulation, covered on the inside with drywall and on the outside with siding. However, this method was slow, labor intensive and costly. In addition, it was not energy efficient because the insulation was interrupted every 16 inches by a stud or rafter allowing heat to easily escape and cold to enter at these points.
In the 1970's, structural insulating panels, commonly known in the industry as stress-skin panels, were developed for use in the residential construction of timber frame homes. The stress-skin panels were nailed to the exterior of the frame members leaving the frame exposed inside the home, thus creating an attractive appearance. These stress-skin panels used in conjunction with a timber frame replaced in many applications the standard 2.times.4 construction of homes. The stress-skin panels were considered stronger than 2.times.4s and were considered to provide better insulating capability.
A stress-skin panel is a panel comprising an outer skin, an inner skin and several inches of rigid foam insulation sandwiched between the two layers of sturdy sheathing material or skins. The outer and inner skins are usually made of plywood, waferboard or oriented strand board (OSB). Both plywood and OSB are commercially available only in certain size sheets. For example, plywood is typically available in 4'.times.8' sheets while OSB is typically available in larger size sheets (up to 8'.times.24'). The foam insulation core located between the two skins is expanded polystyrene (commonly called EPS) or urethane foam, typically 31/2" thick. These panels are typically prefabricated before being installed as part of the walls or roofs of structures like homes, commercial offices, etc.
The stress-skin panels may be manufactured by injecting a liquid urethane between the two skins and allowing the liquid urethane to expand between the skins, the urethane foam adhering to the inner surfaces of the skins without any other adhesives. Alternatively, the foam insulation may be glued or adhesively secured to the outer sheathing layers or skins. However, over time the adhesive used to secure the foam insulation to the two skins may deteriorate if exposed to extreme temperature fluctuations causing the inner and outer skins to sheer apart from the foam insulation.
These stress-skin panels are secured to the heavy timber frame of a structure with long nails or screws known in the industry as pole, barn spikes or deck screws. The length of these nails or screws must be greater than the depth of the stress-skin panels so that the panels may be secured to the exterior surfaces of the timber frame of the structure, the nails or screws passing through the entire stress-skin panel and into the timber frame members.
Stress-skin panels are heavy, restricting the size of the panels. Therefore in order to construct the exterior of a building a large number of panels are required to be affixed to the timber frame of the building. Due to the weight of the stress-skin panels usually the use of a crane is required to lift the panels into place. This requires a great deal of time and manpower and is therefore relatively expensive.
In addition, some type of sealant must be inserted along the joints between adjacent stress-skin panels in order to reduce air and moisture flow through these joints. Alternatively, thin horizontal splines may be used between panels to minimize thermal breaks. Improperly sealed joints or seams can allow moisture to collect and the trapped moisture can eventually cause the materials of the stress-skin panels to swell and deteriorate.
Another drawback to the use of stress-skin panels is that in order to pass electrical wires through the panels, a hollow cardboard tube must be built into the foam insulation layer of the panels in order to create a passageway for the wires to pass through. These tubes passing through the insulation layer of the stress-skin panels reduce the insulating capability of the panels. Additionally, if an electrical outlet is to be located in the stress-skin panel, a portion of foam insulation and a portion of the inner skin must be removed in order to create a place for a conventional electrical box.
In cold climates where a large temperature differential exists between the exterior surface of panels and the interior of the structure, the nails or screws running through the panels may conduct heat and may cause condensation at the heads of the nails or screws. Over time, this condensation may cause the exterior layer of the stress-skin panels to rot which may eventually cause structural failure of the panels.
In addition, utilizing stress-skin panels is expensive. Because the interior layers or skins of the stress-skin panels are usually plywood, another layer of material such as drywall or wood paneling must be placed over and attached to the inner layer of the stress-skin panels to form the inner wall of the home. Similarly, a layer of siding or other material must be placed over the outer skins of the stress-skin panels.
In light of the aforementioned drawbacks of stress-skin panels, a need exists for a panel which is structurally sounder than current stress-skin panels and will not deteriorate or degrade over time due to seasonal temperature fluctuations. A need also exists for a panel which may be made of differing sizes so that an entire wall may be constructed of one panel rather than several pieces of panel. Also a need exists for a panel which does not require the use of long fasteners or nails which pass all the way through the panel in order to secure the panel to a timber frame.
Therefore, it has been one objective of the present invention to provide an insulated wall panel less susceptible to degradation over time than stress-skin panels.
It has a further objective of the present invention to provide an insulated wall panel which does not require long screws or nails to pass through the panel in order to secure the panel to a timber frame of a building.
It has been a further objective of the present invention to provide an insulated wall panel which may be made of many different sizes including the size of one entire wall.